Question 1

Which of the following statements are true of potassium?
I.Hyperkalemia decreases the heart rate.
II.Hyperkalemia decreases the stroke volume.
III.Hyperkalemia causes heart block.
IV.Hyperkalemia increases heart conductivity.

A) I, II, III
B) III, IV
C) I, II, III, IV
D) II, III

I, II, III

Accepted Answer

An excess of potassium ions (hyperkalemia) in the extracellular fluid surrounding cardiac fibers decreases the heart rate and stroke volume. Severe hyperkalemia causes heart block, or the inability of cardiac fibers to conduct action potentials through the heart.

Question 2

Which of the following are properties of the cardiac tissue?
I.Automaticity
II.Rhythmicity
III.Excitability
IV.Contractility

A) I, II
B) III, IV
C) I, II, III, IV
D) II, III

I, II, III, IV

Accepted Answer

All cardiac tissue has the properties of 
(1) automaticity (the ability to depolarize spontaneously), 
(2) rhythmicity (the ability to depolarize spontaneously in a repetitive manner), 
(3) excitability (the inclination to depolarize spontaneously), and 
(4) contractility (the ability to shorten muscle fibers).

Question 3

If AV impulses fail to reach the ventricles after few seconds, what will the heart rate be?&#10;A) 70 to 80 beats/min&#10;B) 15 to 40 beats/min&#10;C) 40 to 60 beats/min&#10;D) 50 to 70 beats/min&#10;

Accepted Answer

If AV impulses fail to reach the ventricles after several seconds, the Purkinje fibers begin to fire at a rate of 15 to 40 times per minute.

Question 4

Which of the following agents are useful in the treatment of ectopic foci?
I.Lidocaine
II.Amiodarone
III.Beta blockers
IV.Calcium channel blockers

A) I, II
B) III, IV
C) I, II, III, IV
D) II, III

Accepted Answer

Antiarrhythmic drugs decrease the irritability of ectopic foci, allowing normal SA nodal pacing. In this group of drugs, lidocaine (Xylocaine) and amiodarone (Cordarone) block Na? channels, decreasing the membrane's tendency to depolarize. Beta receptor blockers such as carvedilol (Cozar) and bisoprolol (Zebeta) depress the myocardium's automaticity, decreasing tachycardia and thus myocardial work. Calcium channel blockers such as amlodipine (Norvasc) and diltiazem (Cardizem) inhibit slow channel influx of Ca⁺⁺ in the SA node and other myocardial cells. This depresses atrial automaticity, slows AV conduction velocity, and decreases myocardial contractility.

Question 5

Which of the following phenomena is responsible for the initiation of muscle contraction?&#10;A) Electrochemical repolarization&#10;B) Membrane depolarization&#10;C) Membrane repolarization&#10;D) Membrane permeability&#10;

Accepted Answer

Membrane depolarization initiates a series of electrochemical events responsible for heart muscle contraction.

Question 6

Which of the following are known effects of catecholamines?
I.They increase the influx of Ca⁺⁺ into the myocardial cell during the plateau phase of the action potential.
II.They activate beta receptors in the cardiac cell membrane.
III.They raise intracellular levels of cyclic AMP.
IV.They raise intracellular levels of cyclic GMP.

A) I, II
B) III, IV
C) I, II, III, IV
D) I, II, III

Accepted Answer

Catecholamines are compounds with chemical structures similar to those of epinephrine and norepinephrine. Such drugs increase the influx of Ca⁺⁺ into the myocardial cell during the plateau phase of the action potential. Catecholamines activate beta receptors in the cardiac cell membrane, bringing about a series of chemical events that raise intracellular levels of cyclic adenosine monophosphate (cAMP).

Question 7

Which of the following conditions are associated with increased heart muscle excitability?
I.Hypocalcemia
II.Hyperkalemia
III.Hypercalcemia
IV.Hypokalemia

A) I, II
B) III, IV
C) I, II, III, IV
D) II, III

Accepted Answer

Hypocalcemia increases heart muscle excitability, causing an effect similar to that of hyperkalemia.

Question 8

Which of the following structures conducts SA nodal impulses to the left atrium?&#10;A) AV bundle&#10;B) Bachmann's bundle&#10;C) Right bundle branch&#10;D) Left bundle branch&#10;

Accepted Answer

The impulse is preferentially conducted along three specialized internodal pathways that eventually converge at the AV node. One of these pathways, Bachmann's bundle, conducts SA nodal impulses directly to the left atrium (Figure 17-12).

Question 9

What explains the AV block caused by vagal stimulation?&#10;A) Increased permeability to K+&#10;B) Increased intracellular K+&#10;C) Increased Na+ inside the cell&#10;D) Increased permeability to Ca+&#10;

Accepted Answer

Acetylcholine (from vagal stimulation) greatly increases K⁺permeability of the cardiac fiber, allowing rapid outward K⁺diffusion. This greatly increases intracellular negativity, hyperpolarizing the cardiac membrane and making depolarization more difficult. This explains why vagal stimulation causes AV heart block.

Question 10

What explains the increase in the SA nodal firing rate caused by sympathetic stimulation? A) Increased permeability to K+ B) Increased intracellular K+ C) Increased Cl- inside the cell D) Increased permeability to Ca⁺⁺

Accepted Answer

Sympathetic stimulation raises the SA nodal firing rate, conduction rate, and overall cardiac fiber excitability. This is explained by the fact that sympathetic postganglionic fibers release norepinephrine, which increases cardiac fiber permeability to Na? and Ca⁺⁺.

Question 11

What is the name of the ventricular rhythm associated with the pacemaker function taken over by the Purkinje system?&#10;A) Ventricular arrhythmia&#10;B) Ventricular escape&#10;C) Dominant rhythm&#10;D) Ventricular ectopy&#10;

Accepted Answer

The answer of What is the name of the ventricular...

Question 12

If the SA node stops firing, what will be the expected heart rate?&#10;A) 70 to 80 beats/min&#10;B) 80 to 100 beats/min&#10;C) 40 to 60 beats/min&#10;D) 50 to 70 beats/min&#10;

Accepted Answer

The answer of If the SA node stops firing, what...

Question 13

Changes in which extracellular ion has little effect on the RMP of cardiac muscle?&#10;A) Na+&#10;B) K+&#10;C) Ca++&#10;D) Cl-&#10;

Accepted Answer

The answer of Changes in which extracellular ion has little...

Question 14

In which of the following clinical conditions are calcium channel blockers indicated?&#10;A) Coronary artery disease&#10;B) Hypotension&#10;C) Asthma&#10;D) Congestive heart failure&#10;

Accepted Answer

The answer of In which of the following clinical conditions...

Question 15

Which of the following may cause premature beats?
I.Local areas of tissue hypoxia
II.Mechanical irritation of the tissue
III.Toxic irritation
IV.Drugs

A) I, II
B) III, IV
C) I, II, III, IV
D) II, III

Accepted Answer

The answer of Which of the following may cause premature...

Question 16

What is the normal sinus rhythm rate?&#10;A) 40 to 59 beats/min&#10;B) 60 to 69 beats/min&#10;C) 70 to 80 beats/min&#10;D) >100 beats/min&#10;

Accepted Answer

The answer of What is the normal sinus rhythm rate?&#10;A)...

Question 17

Which of the following areas of the heart is the most excitable?&#10;A) Bundle branch&#10;B) Purkinje fibers&#10;C) AV node&#10;D) SA node&#10;

Accepted Answer

The answer of Which of the following areas of the...

Question 18

Which of the following are components of the AV nodal system?
I.Bachmann's bundle
II.Junctional fibers
III.Node proper
IV.AV bundle

A) I, II
B) II, III, IV
C) I, II, III, IV
D) II, III

Accepted Answer

The answer of Which of the following are components of...

Deck 18: Cardiac Electrophysiology